Method and apparatus for a power line communications test system

ABSTRACT

A system for testing PLC equipment, network conditions, and protocol performance is provided. Noise measurements can be made at a single point, and protocol traffic, signal levels, and upper-layer parameters of any transmissions by other equipment on the same network are logged. Alternatively, a plurality of units located at different points in the PLC network are at least part of a distributed test system. As a result, coordinated tests can be conducted by multiple nodes, such as point-to-point network transfer function measurement and analysis, estimation of the location of noise sources and system null and resonances, receiver operating curve (ROC) measurements with actual protocol modulation, or any other suitable tests. Preferably, the test devices are able to test using a plurality of PLC protocols. In some devices, PLC protocol-specific modules can be added or removed as desired to increase, decrease or change the test device&#39;s protocol abilities.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/824,379 entitled “METHOD AND APPARATUS FORSWAPPABLE PLC MODULES” and filed on Sep. 1, 2006, the entire contents ofwhich is hereby incorporated by reference.

BACKGROUND

Although various Power Line Communication (PLC) systems have beenintroduced over the years, no scheme has proven reliable and inexpensiveenough to become widespread. Difficulties present in the powerlineenvironment, including noise, severe resonances, complex topologies,large attenuation, and time-varying parameters, have prevented severalschemes from achieving reliable communication. Recent advances intechnology, include inexpensive microcontroller and digital signalprocessors, have improved modem PLC schemes' chances of success.However, PLC success is still not assured, and as a result, a need forPLC-specific test equipment exists. Without such test equipment, itwould be difficult or impossible for a PLC system to be successfullyplanned, deployed, and maintained.

There are two fundamental classes of PLC protocols, specifically controlprotocols and broadband protocols (referred to as Broadband over PowerLines, or BPL). Control protocols are typically low-bandwidth, lesscomplicated, and used mainly for device control and automation, such aslighting control or other similar applications. Control protocolsinclude, but are not limited to, X-10, INSTEON, KNX, UPB, LonWorks, andCEBus. These protocols are generally below 500 kHz, but can be at anysuitable frequency. BPL protocols are high bit-rate, broadband,typically in the range of 1-30 MHz, but can be at any suitablefrequency. BPL protocols include, but are not limited to, HomePlug (1.0,Turbo, and AV), HD-PLC, and OPERA. These protocols can be used forhigh-speed LAN activity such as internet access, streaming A/V contentor any other suitable application. Modulation schemes are complex, andare generally based on orthogonal frequency-division multiplexing(OFDM). The two PLC classes were not designed to work together, but areoften present in the same powerline network, and can interfere with eachother.

SUMMARY

A system for testing PLC equipment, network conditions, and protocolperformance is provided. In one embodiment, noise measurements are madeat a single point, and protocol traffic, signal levels, and upper-layerparameters of any transmissions by other equipment on the same networkare logged. In another embodiment, a plurality of units located atdifferent points in the PLC network are at least part of a distributedtest system. As a result, coordinated tests can be conducted by multiplenodes, such as point-to-point network transfer function measurement andanalysis, estimation of the location of noise sources and system nulland resonances, receiver operating curve (ROC) measurements with actualprotocol modulation, or any other suitable tests. Preferably, such datais available in real-time to the user, and also logged by thedistributed system over time, to track the time-varying nature of thePLC network; however, neither real-time availability nor logging and/ortracking is required. In one embodiment, measurements are controlled bya user via a handheld PDA, cell phone, PC, or any other suitableelectronic device located on-site or remotely. In another embodiment,units are deployed without a central controller. The units beginmeasurements and logging automatically for later download and analysis.

In one embodiment, a testing system is used without an existing PLCinfrastructure. For example, a testing system is used in an engineeringsurvey to see if a particular protocol is suitable for the locationbeing tested. In this case, the system performs noise and networkanalysis functions, as well as protocol-specific tests for one or morePLC protocols. The results can be used to estimate which, if any, PLCprotocols are best suited for the location, how well they will perform,and what modifications may be necessary for a successful deployment orfor any other suitable purpose. As an example, a large commercialbuilding may be instrumented to determine which of the BPL systems (e.g.HomePlug, Opera, or HD-PLC or any other suitable BPL protocol) will bemost suitable, before any deployment is performed.

In one embodiment, a test system is used with an existing PLCinfrastructure. In this case, additional measurements and logging arepossible. Preferably, all network traffic from the existinginfrastructure is monitored, in addition to the normal measurements;however, any suitable amount of monitoring and measurement can beperformed. In one embodiment, the test units send and receive messagesthrough the existing infrastructure for further testing. Such anembodiment can be used to monitor an existing deployment to providequantitative performance measurements, help troubleshoot problem areas,and also possibly survey the building in advance of deploying a secondPLC protocol or for any other suitable purpose. In one embodiment, ifmultiple protocols are already present, more advanced tests areconducted by the units, including simultaneous exercising of theexisting PLC devices to measure interference factors. In anotherembodiment, the test system also monitors the performance of systems inwhich one or more PLC protocols and one or more control protocols areemployed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a flow diagram of the process of testing a network using adevice having swappable modular protocol-specific circuitry inaccordance with one embodiment

FIG. 2 is a block diagram of testing device in accordance with oneembodiment.

FIG. 3 is a flow diagram of the process of testing a network inaccordance with one embodiment.

DETAILED DESCRIPTION

In one embodiment, a test device includes a main controller, a digitalsignal processor (DSP), analog front end (AFE), codec, protocol-specificcircuitry, and one or more communication links. The main controllercoordinates and records measurement functions performed by the DSP,communicates with other device located in the power system, andinterfaces with a host PC or PDA for data viewing, download,initialization, and any other suitable actions. The main controller alsointerfaces to any protocol-specific controller chips associated with thedevice.

In one embodiment, the DSP performs the actual instrument measurementfunctions, including spectral analysis, physical layer protocolanalysis, and/or any other suitable analysis. The protocol-specificcircuitry is preferably the reference design recommended by themanufacturer, and enables the device to send/receive messages in exactlythe same fashion as end-user equipment; however, protocol-specificcircuitry can have any suitable design and can enable any suitablecommunications. The DSP and main controller are coupled to thiscircuitry and can vary protocol parameters (e.g. signal level, sendingspecial test patterns, or any other suitable parameters.) for specialtests.

In one embodiment, the main controller and DSP functions are combinedinto one processor of sufficient capability. In another embodiment, theprotocol-specific circuitry is not needed because the protocol can beemulated exactly by the DSP and its analog front end. In various otherembodiments, multiple protocols are present in one device or are atleast partly implemented in the DSP software. In still anotherembodiment, the device is configured such that the protocol-specificcircuitry is on a daughter circuit board, enabling users to swapprotocol modules as needed. FIG. 1 illustrates the process of testing anetwork using a device having swappable modular protocol-specificcircuitry in accordance with one embodiment. At block 100, the protocolsdesired for testing are determined. At block 110, protocol-specificmodules corresponding to the desired protocols are coupled to thetesting device. At block 120, the testing device tests the network.

A testing device in accordance with one preferred embodiment is shown inthe FIG. 2. In this embodiment, the device 200 is a plug-in unit thatplugs in to a standard 120V receptacle, like many PLC devices. The 120Vline is used to power the unit as well. A 120V pass-through receptacleon the device allows a load to be plugged into it, and the current drawnby this load is monitored. This allows correlations between loadoperation and PLC network operation to be determined.

The device 200 includes a controller module 202. This is the mastercontroller for the entire device 200. It presents a USB device port 204and link interface 206 to a PC or PDA, and can also use the link to talkto other PLC test devices. The controller 202 interfaces to the PLCprotocol processor 208 to send/receive test messages, and also to theDSP 210, to initiate and receive high-speed sample data. It is alsowired to receive input from the zero-cross detector 212, and can controlthe protocol auxiliary circuit 214.

The link module 206 allows the device to communicate with other devicesfor coordinated tests. Tests such as transfer function measurement,point-to-point receiver operating curve measurements, and/or othersuitable tests require coordinated transmission and reception by atleast two devices. This link 206 is typically an RF link such as ZigBee,WiFi, or any other suitable protocol, preferably one supporting ad-hocmesh networks. Since the bandwidth of this link 206 may be less than thePLC protocol under test, special techniques can be used to accuratelysynchronize the devices with it, if desired. In some embodiments,hardwired links (e.g., Ethernet, USB or any other suitable protocol) areused. In other embodiments, a PLC protocol may be used as the link,including the PLC protocol being tested.

In various embodiments, this link 206 may also be used for communicationwith a host PC, PDA, cell phone, or any other suitable device. A usermay connect to the link 206 for real-time control and data display ofthe connected device, and any other devices connected through the linkby the first device, or present on a link mesh network. In otherembodiments, settings and data can be uploaded or downloaded from a useror external controller through this link 206. In one embodiment, thehost is remotely located, and accessed locally through a LAN connection(e.g., via the World Wide Web or any other suitable protocol).

In one embodiment, the USB device port 204 is the preferred link forconnecting the controller 202 to a host PC or PDA. This port 204 allowshigh-speed transfer of recorded data and real-time display or any othersuitable activities. In some embodiments, the port 202 is used totransfer real-time or near-real-time data from the DSP 210 for furthersignal analysis on the PC.

In one embodiment, the Digital Signal Processor 210 interfaces with thehigh-speed codec 216. The DSP 210 can read high-speed A/D samples, andsend out test patterns with the codec D/A. Preferably, these actions areperformed under command of the controller 202; however, the actions canbe performed without controller 202 control. In one embodiment, the DSP210 performs some data processing before sending the results back to thecontroller 202. The DSP 202 also connects to the zero-crossing circuit212 for synchronization, and the auxiliary circuitry 214, in case it isdesirable for the DSP 210 to control the circuitry 214 instead of theARM. In one embodiment, the DSP doesn't do any long-term data storage,but it has scratchpad memory (e.g., a small SDRAM chip or any othersuitable memory) and a serial Flash to boot from or any other suitablememory used for any suitable purpose. An example of a DSP 210 suitablefor one embodiment is a fixed-point Blackfin series from Analog Devices.

In one embodiment, the codec 216 performs high-speed A/D and D/Afunctions, under control of the DSP 210. In one embodiment, aprogrammable logic chip enables the DSP 210 to sample at the full 80 MHzrate or higher rate necessary for BPL protocols. An example of a codec216 suitable for use in one embodiment is the Analog Devices AD9866.This codec 216, along with the DSP 210, implement a tracking generatorfunction.

In another embodiment, a DSP Analog Front End 218 provides amplificationand low-impedance drive to transmit the D/A output of the coded, andalso variable gain for the coded A/D. In addition, it includes acoupling network and bandpass filtering. However, the DSP Analog FrontEnd 218 can have any suitable abilities. Separate AFEs for control andBPL protocols may be used for different embodiments, or a wide-bandwidthcommon AFE may be used, with the DSP 210 performing further bandpassfiltering in software.

In one embodiment, a 60 Hz zero-cross detector/PLL 212 extracts the 60Hz zero-crossing time. It sends the output to both the controller 202and the DSP 210.

In another embodiment, protocol-specific auxiliary circuitry 214 isincluded. The details of module are different for each specificprotocol. For INSTEON, this is an extra PIC, analog mux, and othersuitable circuitry. X10 and the other low-frequency protocols have asimilar circuit. In various embodiments, the high-speed protocols alsohave an analog mux. Some embodiments implement more than one protocol.In one such embodiment, auxiliary circuitry 214 for multiple protocolsis present. This circuitry generally allows the DSP 210 to altercharacteristics of the protocol-specific section, such astransmit/receive signal levels, or any other suitable characteristics,or exercise that hardware directly outside the control of the protocolprocessor 208.

In another embodiment, a PLC Protocol Processor 208, Protocol codec 220and protocol AFE 222 are included. In one embodiment, these componentsimplement the reference PLC protocol design. For INSTEON, it is theINSTEON PIC, plus its analog circuitry—the “AFE” is a transformer and apassive network. The codec is a transmitter transistor and a resistorgoing into the PIC.

For the high-speed protocols, preferably the reference schematic andlayout provided for each one is implemented. Typically these consist ofa processor (usually ARM-based), SDRAM and serial Flash, an AD9866 orsimilar codec, and AFE. One change present in one embodiment for thehigh-speed protocols is a method for the DSP 210 and main controller 202to adjust the transmit level and input attenuation.

Using the specific reference design for each protocol rather thanre-implementing this in the DSP 210 or main controller 202 enables theunit to exactly duplicate the performance of actual protocol hardware,including bugs or undocumented performance characteristics. However, itshould be understood that the protocols can be implemented in less thanexact manners, if desired.

In one embodiment, a Protocol RF 224 is included. If the PLC protocolhas an RF interface 224, this interface 224 is connected to the maincontroller 202. An A/D may be needed to sample the RSSI output from theRF receiver 224. Control protocols such as INSTEON include an RFchannel, which must be incorporated for full protocol analysis.

In another embodiment, a power supply 226 provides isolated 3V, 5V, andother voltages as needed. In still another embodiment, a CT (CurrentTransformer) A/D 228 measures current through the receptacle. Thisenables correlation with load current and unit signal measurements, tohelp determine if specific loads are interfering.

In various embodiments, a 120V Plug, Outlet 230 is used to plug into awall socket. The outlet lets the user plug a load into the device, andthe 120V is passed through to the outlet. The DSP 210 can measure thecurrent of the connected load using the CT A/D 228.

In one embodiment, all data recording is done by the controller 202, andit accordingly includes memory for data storage. However, data recordingcan be performed in any suitable location in various embodiments. Anexample of a controller 202 suitable for use with one embodiment is anARM processor, using SDRAM and Flash memory.

In other embodiments, the device is hardwired into a 120V, 240V, orthree phase 208/120 or 480/277V system. In another embodiment, the basicdevice is incorporated into a circuit breaker form factor, or evenembedded in a fully functional circuit breaker. For devices on mediumvoltage distribution power lines, suitable coupling means is preferred.

In another embodiment, the device also includes an RF analog front-endto measure radiated emissions from PLC networks. The RF analog front-endincludes a suitable internal antenna and/or a connector for an externalantenna, RF gain block, which may or may not have adjustableattenuation, and bandpass filtering. Portions of the standard AFE may beshared with the RF AFE. In this embodiment, the user can test forcompliance with FCC radiated emissions limits.

In another embodiment, the controller function is performed by a PC orPDA or any other suitable device directly. In this embodiment, a USBdevice port is built into the host and a link module is either a hostperipheral (e.g. a USB ZigBee adapter) or embedded in the device. Inanother embodiment, the DSP function also resides in the host PC or PDAor other suitable device, and only the analog front ends, codec, andprotocol-specific hardware reside in the testing device. Communicationfrom the host to the remaining device circuitry is preferably throughUSB or Ethernet links or any other suitable links; however,communication can be implemented in any suitable manner. In oneembodiment, a central host incorporates the controller and/or the DSPfunctions of multiple devices.

In various embodiments, PC host software incorporates post-processing tocompute network parameters based on aggregate data from multipledevices. This software also incorporates network data or topologiesentered by the user, gathered from optical scans of electrical drawings,building plans, or one-line network diagrams, or constructed by thesoftware from measurements of the devices themselves in variousembodiments. In one embodiment, the PC software produces graphs andreports for the user to easily view all measurements.

Operation

The operation of an exemplary 120V plug-in embodiment is describedbelow. It should be understood that other embodiments can have similaroperation, with suitable adjustments for physical differences.

In this example embodiment, installation includes simply plugging one ormore devices into 120V receptacles. Locations are preferably selectedthat cover the entire electrical system to be monitored; however, anysuitable locations can be selected. In addition, any locations where itis known that PLC equipment will be installed (or is installed) ispreferably monitored; however, such monitoring is not required. If thereare loads suspected of interfering with PLC operation, devices arepreferably placed near them, or more preferably, they should be pluggedinto the monitoring receptacle of the device; however, such locating oftest devices is not required. Any existing plug-in PLC nodes arepreferably plugged into the same receptacle as the device, so they areconnected in parallel, however, test devices can be located in anysuitable location and connected in any suitable manner.

As devices are installed, the controllers in the devices are powered up,and begin searching for other devices, and any hosts through the Linkmodule. The installed devices form an ad-hoc mesh network using thisport. A user may use a PDA or PC host or any other suitable device atany suitable time to see the device mesh network topology, and verifythat all installed devices have joined the network.

After the devices are installed, they make protocol and networkmeasurements. These measurements are logged with the default settings,or the previous recording settings. A user can change the recordingparameters at any time, start a new recording, download existing data,or clear the device memory. Preferably, if user is connected to onedevice through either the Link or USB port, the user can alsocommunicate with other devices in the mesh network through that port;however, such communication ability is not required.

The test devices also monitor for existing PLC devices, and join anydetected PLC networks already in place. In addition to coordinatedmeasurements among the devices themselves, the devices also coordinateto send test messages to existing PLC infrastructure, and also monitormessages within the existing PLC network for measurement purposes. Theuser may use the host display to view the status of the existing PLCdevices, or to manually add the devices to an existing network ifrequired.

FIG. 3 illustrates the process of testing a network in accordance withone embodiment. At block 300, one or more test devices are plugged intothe power line network. At block 310, the one or more test devicesdetect the presence of any additional test devices or other PLC deviceson the power line network. At block 320, the one or more test devicesinitiate tests in accordance with whether any additional test devices orother PLC devices are detected.

In one embodiment, the user monitors the network status with the host PCor PDA or any other suitable device. With a PDA, the user may turnvarious electrical loads off and on, and see in real-time the effects onthe PLC network under test. More specific measurements can also beexamined to enable troubleshooting on the spot.

In another embodiment, the user leaves the devices in place for a lengthof time, such as one day or one week or any other suitable period. Thedevices log the selected parameters and the user can download andanalyze the data offline with the host software. This makes it easier toperform analysis of intermittent network problems or to quantifytime-varying network parameters.

In another embodiment, the devices are permanently installed. In thismode, the devices record indefinitely, and are typically initialized tooverwrite older data as new data is recorded; however, any suitablerecording scheme can be implemented, including those that detect acondition of interest and prevent recording over data related toconditions of interest until the user has had an opportunity to view,download, and/or store in long-term storage the data. The recorded datamay be downloaded automatically on a scheduled basis for archival orlong-term studies, or only when a network problem occurs or in any othersuitable manner.

In an embodiment in which the devices are not installed permanently, thedevices can be removed after the desired data has been gathered. Thedata may be downloaded into the host before or after they areuninstalled from service.

In one embodiment, the host software allows for examination of data froma single device and can combine data from multiple devices. Data may beanalyzed separately or combined to compute further statistics.

Measurements

In various embodiments, many measurements are made by a single device.Such measurements can include fundamental measurements such as networkimpedance vs. frequency, noise power vs. frequency, or any othersuitable measurements. Protocol-specific measurements are made invarious embodiments. For example, in the case of INSTEON, noise in theINSTEON package time-slots on the 60 Hz waveform is measured separatelyin one embodiment. In OFDM-based systems, noise is computed separatelyfor each OFDM channel in one embodiment. In various embodiments, thesemeasurements are logged in stripchart format as well as statisticallythrough histograms, and modeled parametrically by the DSP.

In one embodiment, a single test device interacts with an existing PLCinfrastructure. By sending test messages with varying parameters (e.g.power level, timing variations, intentional bit-errors or other physicallayer artifacts), the device can determine Receiver OperatorCharacteristic (ROC) curves for each PLC device. As a result,information about the PLC network is gathered, as is information aboutthe performance of specific PLC pieces of equipment.

The test device also monitors PLC traffic on the network in oneembodiment, logging errors, retries, and other lower and MAC layerprotocol errors. Network problems at the MAC layer are logged. The PLCprotocol block in the device is used for this function in oneembodiment. In one embodiment, the device initiates traffic from one PLCnode to another by sending packets with spoofed identities, or otherwiseconstructing messages that “trick” a PLC node into communicating withanother PLC node, so that measurements may be made.

The test device intentionally injects noise, interfering carriers, orother signals into the powerline network while PLC traffic is occurringin one embodiment. By varying the characteristics of the injectedsignal, the device can determine the network sensitivity to interferenceof various types.

In one embodiment, the test device intentionally transmits messages withdifferent PLC protocols at various power levels, while PLC traffic isoccurring. This enables the device to determine the network sensitivityto other PLC protocols.

Raw waveforms, spectral measurements, or any other suitable measurementsare recorded in various embodiments for post-processing by the host,which may include analysis in conjunction with other devices that werealso recording, but not visible to the original device.

In various embodiment, if multiple devices are installed andcommunicating through a Link port, many more measurements are possible,due to the coordinated action of each controller and DSP.

One such measurement is network transfer function. In general, each DSPmay measure 2-port and multiple-port network parameters (e.g.admittance, impedance, and scattering parameters) from its location inthe network to each of the others. This information may be used by thehost, which receives all the device measurements, to form an overallnetwork model, which can be used to troubleshoot or estimate PLC networkperformance.

Specific transfer function measurements are made with swept-sine orbroadband signal (e.g. white noise, spread-spectrum chip or chirpsequences, etc.) Generally one device would transmit, while all theothers receive; however, any suitable transmission/reception scheme canbe implemented. In one embodiment, the transmitting device measures itspower output, and given its known, calibrated source impedance, theimpedance at that point is computed. The other devices measure theirreceived signal, either in a synchronous or non-synchronous fashion.Synchronization is achieved in various embodiments with clock dataembedded in the transmitted signal, or through the Link port. Since theLink port's bandwidth may be low compared to the bandwidth under test,in various embodiments, phase lock synchronization is used on the timingsignal sent over that link. If a high-accuracy external clock signal isavailable (e.g. GPS) in the embodiment, that may also or alternativelybe used.

Other measurements made in various embodiments include signal to noiseratio (SNR), channel efficiency, Shannon limit for each channel and anyother suitable measurements.

Averaging techniques are used by one embodiment to detect receivedsignals below the nominal system noise floor. This may especially beuseful if transfer functions are measured between devices that aren't onthe same distribution transformer secondary. For example, two adjacentbuildings may have separate distribution transformers. A transferfunction between these two points will include losses from bothtransformers, and would typically require averaging and synchronizationto make the measurement.

In one embodiment, each device can use its protocol-specific hardware tosend valid protocol messages to each of the other devices. By varyingthe message transmission parameters (signal strength, timing, etc.) in amanner similar to the single-device case, ROCs may be mapped from eachdevice to each of the other devices. Any detected PLC nodes on thenetwork may also be included. Each device logs the data collected withits receiver, and a master host can aggregate data from all the devicesto form the overall network measurement in this embodiment.

In some embodiments, all these transmissions are orchestrated by a PC orPDA host. In other embodiments, one test device is declared the networkmaster via an arbitration scheme, and coordinates the transmissions ofall the other devices. In distributed systems where not all devices cancommunicate directly with all others, the master role may be handed fromone device to another to insure as much of the network as possible iscovered. The master device may also be manually selected by the user.

In various embodiments, measurements are recorded on a periodic basis,or additionally, recorded when triggered by certain user-programmableevents. Cross-triggering allows one device to trigger, and then quicklyalert other devices to trigger. Circular buffers of sufficient length toallow simultaneous data recording are present in various embodiments.Periodic triggers are intentionally transmitted by some devices to causeother devices to record synchronously in various embodiments.

In one embodiment, the master device collects all the data from each ofthe other devices, so that only a single device needs to be downloadedby the user. The master device can collect and store the data withoutprompting from the user, or can retrieve the data for the user once theuser indicates readiness to receive the data.

In addition to physical layer measurements, each device makesmodulation-specific measurements in various embodiments. In the case ofone embodiment having an OFDM-based system, this includeschannels-specific versions of the preceding measurements, timingsensitivity measurements, and/or any other suitable measurements. Thetest devices inject signals designed to emulate other PLC protocols inorder to test immunity or coexistence with them in various embodiments.

In various embodiments, measurements are correlated with “position onwaveform” (i.e., determining whether parameters such as transferfunction, noise, or other suitable parameters vary with the timing withrespect to the powerline frequency). These cyclostationary statisticsare computed by the DSP in one embodiment.

In other embodiments, measurements include compliance testing forconducted emissions limits for PLC transmitters. In one such embodiment,the testing device includes a more broad-band front-end to measureout-of-band emissions. Testing includes verification of band notches asrequired in various localities in one embodiment.

If a suitable internal or external antenna is present in one embodiment,radiated emissions compliance is tested, in a similar manner toconducted emissions. In various embodiments, NIST traceability isincluded.

In another embodiment, measurements include demodulated results such asbit-error rates, packet errors, or other suitable measurements. Blocklevel statistics for OFDM in one embodiment include errors in cyclicprefix or other protocol-specific decoding problems. For controlprotocols such as INSTEON, bad checksum or other block errors would berecorded in another embodiment.

MAC layer measurements include collision detection, packet retries,negative acknowledgements, excessive network negotiation traffic, orother suitable measurements in one embodiment. In some cases, networkproblems may exist primarily at this level, especially in the case ofincorrectly configured PLC nodes.

Any side-channel associated with a PLC protocol (e.g. the RF channel inINSTEON) is also monitored in one embodiment. In cases where the RFphysical layer operates synchronously with the PLC physical layer,simultaneous measurements are made in one embodiment. Measurementsinclude received signal strength, bit error rates, ROCs, or any othersuitable measurements.

The DSP in each device occasionally listens for other PLC protocols thatmay appear on the network in various embodiments. For example, a usermay not know that another protocol is in use and interfering with hisnetwork. The device attempts to detect all known PLC protocols whenmessages are received. This activity is recorded.

In various embodiments, the test device operates as a fully functionalPLC transceiver for the specific protocol, performing all networkoperations (bridging, etc.), or it may not fully implement all PLCnetwork protocols. For example, the controller may prevent the PLChardware from participating in bridging activities, becoming a networkmaster, etc., where this would interfere with the measurements. The MACor higher layers may not be fully implemented or enabled, if notnecessary to perform the required signal measurements and computations.

In some embodiments, low-level control of the PLC protocol is notfeasible, due to the reference design architecture. One approach toforce the PLC protocol system in the device to transmit certain messagesis to inject pre-constructed messages into the PLC system codec chain,causing the PLC controller to respond with known transmissions. This canbe done digitally by injecting a digital pattern representing thedesired message between the coded and the PLC processor, or in theanalog domain by having the DSP codec insert an analog signal into thePLC codec's input.

Another approach which may be used in another embodiment is to recordthe digital output from the PLC controller to its codec when it istransmitting certain desired messages. These messages are then replayedinto the codec repeatedly as desired by the DSP or main controller,without using the PLC control system.

Another approach which may be used in another embodiment is to instructthe PLC system to transmit certain carefully constructed bit or blockpatterns. The modulation of these patterns have spectral characteristicswhich are advantageous for spectral measurements. For example, withOFDM, many hundreds of carriers are typically active in parallel,encoding thousands of bits. By carefully choosing the bit pattern, anOFDM output can be arranged so that only certain carriers, or even asingle carrier, is active. By repeating this for many different carrierchannels, a complete network sweep is performed. This technique is usedin a test device of one embodiment which lacks the DSP subsystem and canonly utilize PLC protocol hardware. This technique is also used onexisting PLC hardware in various embodiments.

Time domain reflectometry (TDR) techniques are used in variousembodiments to estimate physical location of powerline network nulls orresonances. This measurement involves measurements from multiple devicesin various embodiments, and uses the host PC or PDA to utilize networkstructure knowledge (wiring diagrams, etc.) to improve the estimate.

In one embodiment, each device attempts to identify the location andsource type of noise sources on the powerline network. Patternrecognition techniques are used to match received noise with a libraryof known noise sources. This library may be stored in the device, in thehost, or accessed dynamically on a remote server over the World WideWeb.

Many different graphs and reports are available through the hostsoftware in various embodiments. High-level reports include overallnetwork performance, both with any existing PLC infrastructure, and withhypothetical additions of various PLC protocol devices. Recommendationsfor optimal PLC protocol, node locations, or any other suitablerecommendations are made, especially as part of a network survey, in oneembodiment. Network performance metrics are compared to previousrecordings to verify current performance against initial installation orother points in time in one embodiment. Estimated location and type ofinterference sources are identified, along with other detected PLCnetworks in another embodiment.

In other embodiments, other reports may indicate network traffic load,the ability to bear more PLC nodes, or any other suitable information.Specific graphs and reports on noise, triggered waveforms and spectralcaptures, are available for detailed analysis in another embodiment.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A test device comprising: a power line interface; a signal detectionunit configured to detect a first signal transmitted on a power linecoupled to the power line interface; a signal generation unit configuredto generate a second signal; a signal transmission unit configured totransmit the second signal on the power line; and a signal analysis unitconfigured to analyze one or more properties of the first or secondsignal.
 2. The test device of claim 1, wherein the signal detection unitis associated with a PLC protocol.
 3. The test device of claim 2,wherein the signal detection unit is removable from the test device. 4.The test device of claim 3, wherein a second signal detection unit isassociated with a second PLC protocol and wherein said second signaldetection unit is attachable to the test device to replace the signaldetection unit if the signal detection unit is removed.
 5. The testdevice of claim 1, further comprising a communications unit.
 6. The testdevice of claim 5, wherein the communications unit is a USB device port,a link module or a protocol RF interface.
 7. The test device of claim 1,further comprising a storage device configured to store data receivedfrom the signal analysis unit.
 8. The test device of claim 7, whereinthe storage device is configured to record data in a circular buffer. 9.The test device of claim 8, wherein the storage device is configured toprevent data associated with a condition of interest from being deletedor recorded over until a user has accessed the data associated with thecondition of interest.
 10. The test device of claim 1, wherein thesignal analysis unit is configured to detect one or more conditions inwhich a first PLC protocol is interfering with a second PLC protocol.11. A method of testing a power line communications network comprising:coupling one or more test devices to the power line communicationsnetwork; analyzing the performance of a the power line communicationsnetwork using a first PLC protocol; and analyzing the performance of thepower line communications network using a second PLC protocol.
 12. Themethod of claim 11, further comprising: detecting which, if any, PLCprotocols are in use on the power line communications network.
 13. Themethod of claim 11, further comprising: detecting automatically thepresence of one or more test devices on the power line communicationsnetwork.
 14. The method of claim 11, further comprising: detectingautomatically the presence of one or more PLC devices on the power linecommunications network.
 15. The method of claim 11, wherein the powerline communications network uses the first PLC protocol and the secondPLC protocol at the same time.
 16. The method of claim 11, furthercomprising: swapping a first PLC-specific module for a secondPLC-specific module in a first one of the one or more test devices. 17.The method of claim 11, further comprising: designating a first one ofthe one or more test devices as a master device.
 18. The method of claim17, wherein the master device controls the operation of the other testdevices.
 19. The method of claim 17, wherein the master device recordsanalysis data gathered by each of the one or more test devices.
 20. Themethod of claim 11, further comprising: analyzing the compliance of thepower line communications network with a government emissionsregulation.
 21. The method of claim 11, further comprising:characterizing one or more electrical parameters of the power linecommunications network.